Probably because your Mi 100 watt car doesn't have enough juice to charge the Mi Supreme. Or the charger output power is not enough to meet the charging needs of the Xiaomi Supreme version. It is recommended to replace the charger with a higher power or use the original charger to charge. At the same time, it is also necessary to check whether the charging cable and interface are normal to ensure that the charging connection is correct.
It may be because your Xiaomi 100 watt car charger does not support the fast charge of the Xiaomi Supreme version, or the charging cable is caused by poor contact. It is recommended that you check that the charging cable is properly connected, try to replace another charging cable, or plug the charger into another device to test. If the problem still exists, it is recommended to contact Xiaomi customer service for professional help.